The present invention relates to a closed secondary battery container, more particularly to a closed secondary battery container comprising plural bonded parts molded from a polyphenylene ether-based resin composition.
Storage batteries or accumulators are widely used as a power source of vehicles such as automobiles, lorries and special vehicles, various types of electric apparatus, industrial equipment, etc. Also, there is a demand for the various types of secondary battery such as lead accumulator, nickel-cadmium battery and lithium battery with concomitant necessity of dimensional enlargement of battery container, diversification of design, light-weight and reduction of thickness. Request for the improvement of moldability, strength, heat resistance and other qualities of the material used for such batteries is being also intensified.
Hitherto, as resin for battery container (or jar), there has been used, for instance, ABS resin (acrylonitrile-butadiene-styrene copolymer). ABS resin has an excellent moldability and a good balance of rigidity, strength and dimensional accuracy, and because of these meritorious qualities, it has been preferentially used, with many satisfactory results, as battery container material. ABS resin, however, has the defect that its water vapor barrier properties are poor and it allows permeation of water vapor. This means that water in the electrolyte contained in a battery is vaporized in long-time use, is allowed to pass through the battery container, and disperse into the ambient atmosphere.
With the recent tendency toward higher temperature and lower humidity use conditions of the batteries and prolongation of battery life expectancy, the environment where the battery electrolyte tends to decrease is steadily increasing. Decrease of the battery electrolyte leads to a rise of internal resistance of the battery, thereby giving serious adverse effect to its discharge performance. Therefore, the use of a resin as much impervious to water vapor as possible is desired as battery container material.
Polyphenylene ether resin is popularly used as material of commercial products in many fields of industries, such as electronic parts, electric appliances, automobile parts, etc. because of its excellent mechanical strength, heat resistance and dimensional stability. Recently, its utilization as material of closed-type secondary battery container is studied for making use of its excellent water vapor barrier properties and acid resistance in addition to the above-mentioned properties.
A closed secondary battery usually comprises plural parts such as container body and cover, and these parts need to be bonded to each other with an adhesive or bonding agent to secure a hermetically closed condition in use of the battery. The bonding agent used for this purpose is required not only to meet such normal quality requirements as bonding strength and heat resistance but also to be resistant to the specific acid and alkali used for the electrolyte.
In the case of using such polyphenylene ether resin as battery container material, however, there arise problems because this resin is inferior to ABS resin in bonding strength, the bonded portions of the container could peel off when an internal pressure is exerted to the container during charging or discharging, or the container could be broken or cracked from its bonded section when, for instance, it is let to fall down.
As a result of the present inventors earnest studies, it has been found that when producing a closed secondary battery container, by bonding together the plural parts molded from a polyphenylene ether resin composition through a specific bonding agent, such a battery container is highly resistant to internal pressure and impact and capable of maintaining its normal performance constantly for a long time.
The present invention has been attained on the basis of the above finding.